C# – Automapper Object reference is required for the non static field, method or property

.net-core-3.0automapper-9c

I recently Upgraded my .net core to 3.0 and Automapper from 6.2 to 9.0. Now the automapper is throwing the following compile time error when using mapper.map inside mapfrom function.

CreateMap<DomainEntity, destination>()
            .ForMember(dest => dest.userId, opt => opt.MapFrom(src => Mapper.Map<.UserInfo, string>(src.UserDetails)))
            .ForMember(dest => dest.alertKey, opt => opt.MapFrom(src => src.Key));

An object reference is required for the non-static field, method, or property 'Mapper.Map(xxx)'

Automapper has removed static keyword in its new upgrade for Mapper class Methods.

Best Answer

Your question was specific to profile of the mapper but the post title ties with the below issue too. In my case, it was not exact same problem but I was getting same error. So I wanted to share this for anyone who had same error like mine.

Looks like Automapper is not a static class anymore. So you will need to instantiate it. To be able to do that, you will need to install the package :

Install-Package AutoMapper.Extensions.Microsoft.DependencyInjection

Once it is done, than you can inject IMapper instance in your class like:

public MyClass {

     private readonly IMapper _mapper;

     public MyClass(IMapper mapper){
          _mapper = mapper;
     }

     public DtoType SomeMethod(EntityType entity){
          // do your mapping..
          var myDtoType = _mapper.Map<DtoType>(entity);
     }
}

Important part is, it may look like a bit of black magic since you never registered IMapper in the ServiceCollection. But the Nuget package and the call to “AddAutoMapper” in your ConfigureServices takes care of all of this for you.

PS: didn't write the code on VS but you got the idea.

Related Solutions

C# – the difference between a field and a property

Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class.

public class MyClass
{
    // this is a field.  It is private to your class and stores the actual data.
    private string _myField;

    // this is a property. When accessed it uses the underlying field,
    // but only exposes the contract, which will not be affected by the underlying field
    public string MyProperty
    {
        get
        {
            return _myField;
        }
        set
        {
            _myField = value;
        }
    }

    // This is an AutoProperty (C# 3.0 and higher) - which is a shorthand syntax
    // used to generate a private field for you
    public int AnotherProperty { get; set; } 
}

@Kent points out that Properties are not required to encapsulate fields, they could do a calculation on other fields, or serve other purposes.

@GSS points out that you can also do other logic, such as validation, when a property is accessed, another useful feature.

C# – CS0120: An object reference is required for the nonstatic field, method, or property ‘foo’

It looks like you are calling a non static member (a property or method, specifically setTextboxText) from a static method (specifically SumData). You will need to either:

Make the called member static also:

static void setTextboxText(int result)
{
    // Write static logic for setTextboxText.  
    // This may require a static singleton instance of Form1.
}

Create an instance of Form1 within the calling method:

private static void SumData(object state)
{
    int result = 0;
    //int[] icount = (int[])state;
    int icount = (int)state;

    for (int i = icount; i > 0; i--)
    {
        result += i;
        System.Threading.Thread.Sleep(1000);
    }
    Form1 frm1 = new Form1();
    frm1.setTextboxText(result);
}

Passing in an instance of Form1 would be an option also.

Make the calling method a non-static instance method (of Form1):

private void SumData(object state)
{
    int result = 0;
    //int[] icount = (int[])state;
    int icount = (int)state;

    for (int i = icount; i > 0; i--)
    {
        result += i;
        System.Threading.Thread.Sleep(1000);
    }
    setTextboxText(result);
}

More info about this error can be found on MSDN.

Best Answer

Related Solutions

C# – the difference between a field and a property

C# – CS0120: An object reference is required for the nonstatic field, method, or property ‘foo’

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